Distillation of tar



July 12, 1927.

1,635,896 J. s. MORGAN ET AL DI STILLATION OF TAR Filed June 1. 1922 I '//fl///////////////////////////////fl///////////////////////////////////////// //W Patented -July 12, 1927.

UNITED STATES g ,635,-896 PATENT OFFICE.

JOHN srANLEYMoRGAN AND DOUGLAS aman, or LONDON, ENGLAND, ASSIGNORS 'ro 'I'll-!ERMAL INDUSTRIAL AND CHEMICAL (T. x; c. RESEARCH COMPANY LIM- ITED, or' LoNDoN, ENGLAND. u

DIsmLLATIoN or na.

Application med June 1922, serial No. 5,102, and in Great Britain June 7, 1921.

The chief difliculties in the distillation of tar occur in the early and final stages. At first the tar contains water and light oil and these constitueits cause frothing, which oc- 6 curs as the temperature of the tar rises. This eccssitates slow and' careful heating or heating under pressure. In'the final stages the pitch is a highly viscous liquid and uniform and sufiicien't heating so as to expel 10 all oil, is diflicult to bring ahout owing to poor conductivity and sluggish convection currents. i

By our method of operation we 'overcome these difficulties in a continuous manner and finally have to provide for the re-distillation of an oil 'which does not frothor leave any pitch as resdue. y

According to our invention, we feed the crude tar, preferably"preheated, under the surface ofa mass of molten metal maintained at a temperature suitable for volatilizing the volatile constituents, with the exception of anthracene, which remains for the greater part in the residue of distillation, this resit ue constituting semi-pitch; for this purpose lt is preferred to maintain the molten. *metal at a temperature of about 275--290 C. .We withdraw the semi-pitch :from the still, and furthertreat it by rasing 3 lt to a temperature 'at which it ives u the anthracene which it contains. e e er to conduct this latter treatment with t e aid of super-heated steam in the form of a jet which breaks up the semi-pitch into spray; the

85 anthracene'is carried over by the steam and recovered, andleaves as residue pitch. The period of time during which the tar is under the metal is short but is suflicient to vaporize the water and li 'ht oils, which may, f de- 40 sired, be removed from the still by-a sepaate outlet. We prefer to work n such a way that all the original vapours leave the primary still through one outlet, since by this means we have the advantage of steaming'the semi-pitch with the water `vapour which is formed while -thetar is' immersed in the molten metal. This enables us 'to work at a somewhat lower temperature and assists the removal of the heavier oils. The dehydrated tar is` caused to'flow over the molten metal surface, takin it may be a circuitous route owing to ba es, and is here de rivedof all the oils which are volatile be ow the temperature of the' molten metal,

"having the next higher tem )erature.

say 27 to 290 C. It is preferable that. the resdue in the still should be' asthi'a layer as possible.

The volatile constituents ofthe tar leave i the still at a substantially uniform rate and may be fractionally condensed if desired, but we find that .fractional condensation involves such large scrubbing vessels that it can only be economicall applied when the difference between the ractionating temperatures is very considerable; This is the case with the li ht fractions and' the creosote fraction. W e therefore prefer to lead the volutile constituentsinto a relatively small fractionul condenser, the head.of` which may be kept at about 120 C. by means of the incoming tar which is thus preleated. The vapours leaving at about 120 C. consist almost entirely of water va our and light oils. may be some oil oiling above 180 C. that is, creosote oil, but there will be no light oil left in the li'uid which condenses in the fractionator w iich is the im ortant point. The condensate from the E'actionator is now led into a small secondary still also containing molten metal which is kept hot b 7 means of waste heat from the primary still. This secondary still is kept at about 230 3. and removes all theremaining constituents which boil up to 230 C. The distillate is cooled and collected. The residue constitutes another fraction boiling between `230 C. and 270 C. e

If desired these temperature limits may be sub'ected to considerable variation.

he light oil which is always snbjected to re-distillation is treated in a subsidiary still where it is heated by means of the latent ,heat of condensation of one of the hi her fractions. In this way a considerable lieat econony is efl'ected and a continuous process is substituted for the present intermittent processes. i v

If desired, we ma condense all or part of the vapours from the primary still and re` vaporize them in secondary stills leading the condensate into the'lighest temperature still first condensing the vapors from each still and leading the condensate into the sitlill ie number'of separate stills, an the tem eratures at which they are maintained wi l, of course, dependon the number of frnctions it is desired to obtain. In this case, we col- There i lect the residues from each still as the fraetons desired.

This method has some advantages but more heat is required and more condenser space is necessary. Furthernore, corrosion occurs to some ex'tent whenever water condenses owing to the presence of a certain quantity. of ammonium chloride Itis desrable, therefore, to limit the points of attack by removing the water at the first condensation and for this reason we prefer the combined fractional condensation followed by re-distillation already described.

It is necessary to provide molten metal bottoms to .the secondary stlls in case they should for some reason run dry. The nolten metal would in such circumstances prevent local overheating and dam-age to the still.

The preferred method of Operating according to the invention is as follows:--

The-tar is treated by means of the molten metal bath and the temperature of the residue is kept at about 275-290 C. This semipitch flows into the base of atower where a jet of superheated steau bre-aks it up into a spra The finely divided pitch give up its ant racene in presence of the stean and the vapour is ledto a condenser. This condenser is kept at about 100C.-104 C. and serves to condense all the anthracene but allows the steam to pass on. This steam is caused to flow through the superheater again by the action of a jet of high pressure steam and the mixture of high and' low .pressure steam thus produced is used to spray the pitch. By this means a eonsiderable economy in steam and therefore fuel consumption is efl'ected. The steam acts only as a carrier and there is no objection to the re-use of the steam at a lower pressure. It is sometimes desirable to insert the jets of high pressure steam actually in the spraying tower so that the pitch is sprayed and the low "pressure steam induced at this point; the advantage of this method consists ina more perfect subdivision of the pitch.

It s necessary to superheat the' steam which is being used to as great an extent as is possible with the flue gases since only the sensible heat of the pitch and the steam is available to supply the' latent heat of the anthracene fraction.

It is possible, however, to operate 'without superheating if provision is made for 'addin heat to the semi-pitch from 'some extern source.

The accompanying diagram illustrates the invention 4 Referring to the drawin the molten metal bath still a is set in a urnace I and its temperature maintained at about %75- 290 C. I The tar is pumped from a container c by a pump d and after passing throu h a heat exchanger e and a jacket to the ractionatin column f, enters the still a beneath the sur ace of the metaltherein. Here it loses all constituents which boil below the aforesaid temperature, which pass as mixed vapours into the column f. The temperature of the latter being kept at about 120 C. by the tar passing through the jacket, the vapours which leave the column consst almost entirely of water vapour and light oils: these vapours pass through the heat exchanger e and flow by pipe g to the condenser h.

The constituents free from light oil which condense in the column f flow throu h pipe i, heat exchanger k and pipe Z into t e secondary still m. which is also a molten metal bath and :230 C. The vapours from this still pass through the heat exchanger k and pi e n to the condenser o, while the residue rom the still fiows into a cooler p.

The seni-pitch leaves the still a by pi e q is kept at a temperature about` to enter a tower 1' where it is spraye by superheated steam. The anthracene and ste-an passes by pipe s to the condenser t which is at about 100 to l04 C. so that the anthracene condenses and is recovered while the stean is returned to the tower 9" through a superheater; the arrangements for this are not shown in the diagran. The pitch from tower 7' is withdrawn through the pipe u.

Having thus described the nature of the said invention and the best means we know of carrying the sane into practical eflect, we claim 1-- 1. A process of distillin tar, which consists in feeding the tar un er the surface of a mass of molten metal, maintaining the te'nperature of the molten metal at a tem erature adapted to vaporize the more vo atile constituents and to leave as residue of the distillation semi-pitch containing the ater part, of the anthracene present in t e tar withdrawing from the surface of the meta the semi-pitch produced and raising the temperature of the semi-pitch to that at which it gives up the anthracene which it contains. u 2. A process of distillin tar, which consists in feeding the tar un er the surface of a mass of molten metal, maintaining the temperature of the molten metal at a temperature adapted to vaporize the more volbelow 290 C., withdrawing from the surface of the metal the semi-pitch roduced and raising the temperature of t e semipitch to thot at which it gives up the anthracene which it contains.

4. A process of distillin tar, which consists in feeding the tar under the surface of a mass of molten metal, naintainin `the temperature of the metal above 27 5 and below 290 C., withdrawing from the surface of the metal the semi-pitch produced and causin the semi-pitch to meet a jet of superheatec steam so that it is broken up into spray and gives up its anthrecene to the steam.

5. A process of distillin tar, which consists in feeding the tar under the surface of a mass of molten metal, naintaining the temperature of the molten metal at a temperature about 275 C. and below 290 C., mantaining the vapors evolved at a temperature ad'apted to condense at least a, part thereof, thereafter bringing the condensate into. contact with another mass of molten metal at a temperature adapted to vaporize a f'action of said condensate, and to leave as unvaporized residue another fraction, withdrawing from the surface of the firstmentioned metal the semi-pitch produced and raising the temperature of the semipitch to that at which it gives up the anthracene which it contains.

6. A process of distillin tar, which consists in feeding the tar un er the surface of a mass of molten metal, maintaning the temperature of the molten metal 'at a temperature about 275 C. and below 290 C.,

maintaining the vepors evolved at a temperature adapted to condense at least a part thereof, thereafter bringing the condensate into contact with another mass of molten metal at a. temperature adapted to vaporize a fraction of said condensate, and to leave as unvaporized residue another fraction, withdrawing from the surface of the firstnentioned metal the semi-pitch produced and causin the semi-pitch to meet a jet of superheate stearn so that it is broken up into spray and gives up its anthracene to the steam.

7. A process of distilling tar con rising the following steps-( 1) preheating tie tar; (2) feeding the pre-heated tar under the surface of molten metal maintained at a temperature above 2759 C. and below 290 0.; (3) cooling the vapours which leave the tar to a. temperature about 120 0.; (4 feedmg the liquid condensate from step (3) beneath the surface of molten metal maintained at a temperature about 230 0.; (5) condensing the vapours not condensed in step (3); (6) condensing the v'apours from step (4 (7) withdrewn the non-vaporized residue from the sur ace of the met-el in step (4) (8) withdrawing the non-vaporized resi ue from the surface 'of the metal n step (2) and (9) causing the withdrawn residue in step (8) to meet superheated steam so as to volatilize anthracene and obtain hard. pitch.

In testimony whereof we have signed our names to this specification.

JOHN STANLEY MORGAN. DOUGLAS RIDER. 

